Transmissions that have constraints on the size of the diameter of gears due to space limitations, but which are also required to transmit significant power, have presented difficult design problems. An appealing concept for the solution to this problem is the use of multiple gears on a common shaft. The multiple engaging gears on a common drive shaft and a common driven shaft would transmit a relatively low load. However, the combined load transmitted by the multiple engaging gears on a common drive shaft and a common driven shaft would be relatively large. This apparent simple theoretical solution has proven to be impractical because of the difficulty in achieving even load sharing among engaging gears.
Due to gear manufacturing tolerances, multiple gears on a drive shaft are not likely to be perfectly aligned with the corresponding multiple gears on a driven shaft. When a load is applied, sets of engaging gears on the drive and driven shafts are not likely to simultaneously mate. This non-perfect alignment results in gears on the drive and driven shaft to engage unevenly. This results in one or more engaging sets of gears to be loaded higher than their design load with resulting premature failure due to excessive load or wear. Minor misalignments in the drive and driven shafts and shaft flex also are factors contributing to the uneven loading of engaging multiple gears on the drive and driven shafts.
Very precise tolerances were required to successfully construct a transmission having multiple gears on a common shaft. As is appreciated by one skilled in the art, the more precise the tolerances required, the greater are the manufacturing costs. Because of these tolerance-cost considerations, transmissions having multiple gears on a drive shaft and driven shaft were generally impractical.
This problem in prior art transmissions was first solved by the present inventor as disclosed in U.S. Pat. No. 5,927,147 to Morrow titled Power Sharing Gear Sets, the entire disclosure of which is incorporated by reference herein. U.S. Pat. No. 5,927,147 is directed to a gear transmission wherein pairs of helical gears (a helical gear being a gear having a helical cut on the outer diameter of the gear) are mounted on a drive shaft for rotation by the drive shaft and axial movement on the drive shaft. The pairs of helical gears mounted on the drive shaft engage corresponding pairs of helical gears mounted on a driven shaft for rotating the driven shaft and for axial movement on the driven shaft. U.S. Pat. No. 5,927,147 achieves even load sharing amongst engaging gears. U.S. Pat. No. 5,927,147 does not include the use of helical cut splines on the drive and driven shafts.